Columbia's state environmental agency said that roughly 80 gallons of oil was spilled into the Columbia River by a vessel near Kalama.
The Nord Auckland, a 618-foot ship flagged in Singapore, reportedly spilled the waste oil during an internal oil transfer on Thursday morning.
The ship, owned and operated by Denmark’s Norden, was at anchor when an apparent operator error led to the spill of substances which were intended to be incinerated.
The multi-team response was coordinated by the Washington Department of Ecology and the US Coast Guard (USCG).
Department of Ecology documents say the cause is still under investigation but the source of the spill was secured and no additional spills are expected.
Ecology spokeswoman Krista Kenner says 80 gallons is the amount reported by the vessel and that the spill on deck was larger than that.
U.S. Coast Guard documents say oil was seen near shorelines and wildlife areas but so far no significant accumulations have been found.
Launched in 2010, the Nord Auckland is a bulk carrier displacing 22,683 gross register tons, according to the website marinetraffic.com. It was bound to Kalama to load wheat for export when the spill occurred, according to a Columbia River shipping website.